site: render diagrams for the dark theme

The diagram SVGs are light-theme images loaded through <img>, so they
cannot read data-theme. Invert and hue-rotate them when the theme is dark;
the white card turns near-black and the blue palette stays blue.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ryansolid

osmium/src/index.css

@@ -80,6 +80,13 @@
 	img {
 		@apply rounded-xl;
 	}
+
+	/* Diagrams are hand-drawn light-theme SVGs served as images, so they cannot
+	   read data-theme themselves. Invert and rotate hue in dark mode: the
+	   white card turns near-black and the blue palette stays blue. */
+	html[data-theme*="dark"] img[src^="/images/diagrams/"] {
+		filter: invert(0.92) hue-rotate(180deg);
+	}
 }
 
 .shiki.material-theme-ocean {